Continuous modification of polypropylene via photoinitiation

Abstract

A twin screw extruder was used for continuous modification of polypropylene (PP) via UV radiation. Long chain branches were incorporated in the PP backbone to modify its rheological properties. Benzophenone (BPH) as photoinitiator and trimethylolpropane triacrylate (TMPTA) as coagent were utilized during PP photomodification. Radiation was carried out after mixing in the extruder on solid stretched strands with approximately 0.3 mm thickness. The effects of photoinitiator concentration, radiation time and coagent presence were studied via a replicated two-level full factorial design of experiments. It was shown that photomodification of PP can be done continuously. Formation of long chain branches (LCBs) in the experimental runs was confirmed via rheological measurements. Gel content of the samples was also measured. It was found that long chain branches can be formed in PP with and without TMPTA at certain processing conditions. The amount of gel in the samples prepared with TMPTA was higher; however, the gel content could be controlled by manipulating BPH concentration and radiation time.

An Overview of the Potential of UV Modification of Polypropylene

“…Furthermore, GPC test results also showed that the radiated sample after gel exclusion had about 0.26 branches per polymer molecules (weight average). These GPC results are not shown in this overview (for the sake of brevity) but can be found elsewhere . All these results confirm the mechanism suggested in Table f for formation of XPP, and show that XPP samples contain considerable amount of LCBs as well as gelled structures.…”

“…It has been found that TMPTA has very fast kinetics and can be successfully utilized to form long chain branched structures in PP at the presence of either photoinitiators or peroxides. Utilizing TMPTA along with photoinitiators can result in formation of significant amount of gel, which makes formation of XPP a straightforward process …”

“…In these reactions (radiation inside the extruder) formation of long chain branched structures was only possible in the presence of coagents; without the aid of coagents, only degraded PP was formed . The other possible drawback of melt radiation inside the extruder is that UV only penetrates through the surface and this causes inhomogeneities in the modified mixture …”

“…[24] The other possible drawback of melt radiation inside the extruder is that UV only penetrates through the surface and this causes inhomogeneities in the modified mixture. [25] In order to avoid the disadvantages of reactive extrusion and radiation of the molten polymer in the extruder, the extrudate was radiated after solidification. In this method, PP and BPH were mixed in a twin screw extruder and radiation was carried out after solidification of this mixture in the cooling bath.…”

Impact of rapid ozone degradation on the structure and properties of polypropylene using a reactive extrusion process

“…[8][9][10][11][12] The decomposition is known to lead to the formation of secondary products such as alcohols and ketones, which can impart a disagreeable odour and taste characteristics to the resin. [26][27][28] Mechanical degradation and oxidation degradation are two other ways that could induce the molecular weight decrease of PP. 14, 15 The common element is the steady peroxide addition rate.…”